1. Field of the Invention
The present invention relates to an oscillating device for oscillating a ring mold which supports the peripheral edges of a sheet glass in a circular or similar motion within a horizontal plane.
2. Description of the Relevant Art
According to one known method of quenching a sheet glass, the peripheral edges of the sheet glass which is heated to a high temperature are supported, from below, by a ring mold, and oscillatory motion is imparted to the ring mold to move the same in a circular, elliptical, or linear path within a horizontal plane while cooling air is being applied to the surface of the sheet glass.
FIG. 6 of the accompanying drawings shows a conventional oscillating device for imparting such oscillatory motion to a sheet glass. The illustrated oscillating device has a first support plate 102 movably disposed on a base 100 through a slide bearing 101 for movement in the direction of an X-axis (i.e., a horizontal direction in FIG. 6), and a second support plate 104 movably disposed on the first support plate 102 through slide bearings 103 for movement in the direction of a Y-axis (i.e., a direction normal to the sheet of FIG. 6). A ring mold 105 is supported on the second support plate 104. The first support plate 102 is moved in the X-axis direction by a motor 106 through a ball screw 107, and the second support plate 104 is moved in the Y-axis direction by a motor 108 through a ball screw 109.
For example, the ring mold 105 may be oscillated in an elliptical path which, as shown in FIG. 7, starts from an origin o to a to b to c to d to a to o. Between the points o and a, only the motor 106 is energized to move the ring mold 105.
The ring mold supports the peripheral edges of a sheet glass thereon. If the ring mold failed to return to the original position, the supported sheet glass would be displaced out of a desired position. Therefore, the oscillating device is arranged such that it will finally move the ring mold back to the origin o at the end of an oscillating cycle. However, the conventional oscillating device tends to fail to move the ring mold 105 along an exact path and also to return the ring mold 105 back to the origin because of a backlash between the threads of the ball screw 107 and a nut threaded thereover, different weights of the two systems movable along the X- and Y-axes, and a failure to accurately control the timing to start the two motors 106, 108.
Another drawback with the conventional oscillating device is that the ball screw 107 has a short service life since it is rotated about its own axis repeatedly in alternately opposite directions by the motor 106 which is reversible.